PROJECT SUMMARY/ABSTRACT African-Americans (AA) present with overall more advanced prostate cancer (PCa) than European Americans (EA). Even when socioeconomic factors are controlled for, AA have a worse prognosis than EA at the same stage of cancer. Furthermore, 35% of AA patients assigned to active surveillance rather than radical treatment eventually have to undergo treatment due to disease progression, compared with only 15% of EA patients. In preliminary studies, we have observed higher activation of an entire anti-viral immune response pathway in tumor-adjacent stroma of EA PCa patients when compared to AA. This pathway begins with the activation of endogenous retroviruses, which are ubiquitous in the human genome but are normally DNA methylated and inactive. In EA prostate cancer stroma, ERVs are activated, with higher expression and lower DNA methylation than in AA. When activated, ERVs produce dsRNA that, in turn, activates type 1 interferons (IFNs), which are also higher in EA than in AA prostate cancer stroma. IFNs then activate expression of interferon-stimulated genes (ISGs), which are more highly expressed in EA but not AA stroma. Finally, we see higher expression levels of markers of activated dendritic cells (DCs) in EA but not AA stroma. DC are immune system cells that are an ultimate target of the IFNs and can be anti-tumor. We hypothesize that epigenetic control of anti-viral immune response pathways in prostate stromal cells contributes to the observed racial differences in PCa progression. High expression levels of ERVs and ISGs correlate with favorable disease outcome in several solid tumors, making this anti-viral pathway a potential target for an activation therapy. Anti-viral immune response pathways can be activated using the nucleotide analog 5AzaC, a methyltransferase inhibitor, which has been used to treat solid tumors including breast, ovarian and colorectal cancer. We have developed a unique resource of tumor-adjacent cancer-associated fibroblasts (CAFs) from 25 AA and 25 EA patients, which allows us, for the first time, to experimentally test antiviral immune response pathways in different races. In Aim 1 we will investigate whether 5AzaC and/or type 1 IFN enhance the activity of ISGs in CAFs of AA and EA. We will also characterize the differential effect of AA and EA CAFs on the development and growth of prostate tumor cells and the effect of 5AzaC and/or IFN treatment on the stromal phenotype when exposed to tumor cells. In Aim 2 we will explore whether DCs co-cultured with AA CAFs and EA CAFs display differences in IFN production and T-cell activation. In Aim 3 we will investigate protein markers for ERVs, IFNs, ISGs, and activated DCs by immunohistochemistry of tumor samples. We will determine whether expression differences in these markers can result in a prognosticator of outcome and efficacy for PCa treatment. For this aim, we will employ 80 AA and 80 EA cases embedded in FFPE, hundreds of cases preserved as Tissue MicroArrays (TMAs), and 13 pairs of AA and EA cystoprostatectomies (controls). Overall, our studies will impact PCa management of AA patients, including strengthening of criteria for enrollment in active surveillance and initiation of possible new therapies.